Film delamination due to subsequent thermal processing is a problem that plagues the semiconductor manufacturing industry and other applications in which film deposition is utilized. Commonly, the problem is due to a poor adhesion force between the deposited film and the material upon which the film is deposited. This problem can occur when the film is the same as the material upon which it is being deposited or different than the subjacent material. The poor adhesion between the film and the material upon which it is deposited, causes delamination such as peeling, cracking and/or blistering of the film during subsequent thermal processing such that takes place at an elevated temperature in the vicinity of 300° C. or greater. For example, this phenomena is experienced when a stack of amorphous silicon films are formed. Amorphous silicon (a-Si) films may be hydrogenated to passivate dangling bonds and the hydrogenated amorphous silicon is designated a-Si:H. The aforementioned adhesion force is particularly weak at the a-Si:H/a-Si:H interface formed between two films. The upper a-Si layer will delaminate after a subsequent thermal cycle due to residual stress (compressive) formed at the interface due to the deposition characteristics and conditions of the upper a-Si:H film and also due to hydrogen diffusion at the interface. This problem is particularly egregious when the film is relatively thick, such as 1 micron or greater. The problematic subsequent thermal cycling is difficult to avoid since semiconductor devices typically undergo a number of thermal cycling processes during their manufacture. For example, the formation of a passivating film such as silicon nitride typically takes place at an elevated temperature and for a sufficient time to effectuate delamination.
Although described in conjunction with an a-Si film, the delamination problem occurs in various films used in semiconductor device and solar cell fabrication.
There have been various approaches that address this delamination problem. These efforts include fine-tuning the film deposition conditions to minimize the compressive stress of the deposited film, instituting various cleaning procedures prior to the film deposition process, de-gassing prior to the film deposition process, instituting a sticking layer prior to the film deposition process, and roughening the surface upon which the film will be deposited. The effectiveness of these conventional procedures is limited and many of the aforementioned procedures for addressing the problem, are unsuitable for various manufacturing environments.
Even when only partial delamination occurs, contamination from the cracking, peeling, blistering delaminated film degrades the quality of the entire semiconductor device, even in areas where the film does not delaminate. It would therefore be advantageous to provide a process and structure for preventing film delamination during subsequent thermal processing operations.